1. Field of Invention
This invention relates generally to the field of movable and stackable seating. More particularly, this invention relates to chairs having a self-adjustable back support while retaining a stackable function.
2. Description of Related Art
Prior chairs having a flexible backrest frame have provided frame members with spring members connected internal of seat tube members for control of movement of the backrest frame of the chair. A typical flexible backrest is illustrated in U.S. Pat. No. 5,039,163, issued to Tolleson, which discloses a chair including depending leg members and a hollow support frame having members with open ends terminating beneath the seat assembly of the chair. The chair includes a pair of hollow backrest frame members having open frame ends extending beneath the seat assembly for alignment with respective open ends of the support frame members. Each open end of the respective frame members includes at least one flexible spring member inserted therein. Prior configurations of spring members allow insertion of opposed spring member ends into opposed and aligned open frame ends, with each spring member being aligned with the frame ends and extended to fill any gap between the respective back frame members and support frame members. Therefore, replacement of the spring member required full disassembly of the chair frame and removal of each inserted spring member end. In order to prevent each spring element from excessive flexing during reclining movements of the chair backrest, the spring member ends have been typically enclosed by pairs of U-shaped brackets of metal that limit the range of angular movement of each enclosed spring member, thereby limiting the reclining movements of the chair backrest. Additional pairs of spring members and U-shaped brackets have been required to be added for rigorous use. The additional pairs of spring members are typically position parallel to each first set of spring members with associated enclosure by U-shaped brackets of greater width or depth, thereby requiring an increased width or depth of the support frame members to accommodate the additional spring members and brackets.
Another example of a chair having a flexible backrest frame is illustrated in U.S. Pat. No. 6,471,293, issued to Ware et al., which discloses a chair frame including respective pairs of seat support leg members having a front spring reinforcement bar interconnected therebetween, and including a back support frame having lower ends with a rear spring reinforcement bar interconnected therebetween. Movements of the back support frame relative to the seat support leg members are regulated by a pair of spring members connected to span between front and rear spring reinforcement bars. Limits to movements of the spring members and back support member are provided by a seat cushion having a two-piece, split platform member with a front portion and rear portion moved relative to each other in response to flexing of spring members. A plurality of bolt brackets affix the spring members opposed ends to each front and rear spring reinforcement bar and to front and rear split platform members of the seat cushion. Repetitive rearward and forward movement of the back support frame flexes each spring member and moves the seat split platform members relative to each other, thereby repetitively flexing the seat cushion.
There is a need for a stackable flexible chair back that provides a spring member assembly attached between a back frame and a seat assembly having a seat cushion thereon, and configured to limit the back frame rearward movement and forward movement while minimizing contact between the spring member assembly and the seat cushion thereby reducing fatigue of the fabric covering the seat cushion. There is a need for a stackable chair having a flexible back frame connected to a seat assembly by a spring mechanism having a minimal number of parts that are readily replaceable to extend the useful life of the stackable chair.